1. Field of the Invention
The present invention relates to an imprint apparatus, and more particularly, to an imprint apparatus in which a mold on which a pattern is formed, and an imprint material disposed on a substrate surface are pressed against each other, thereby the pattern of the mold is transferred onto the imprint material.
2. Description of the Related Art
Nanoimprint is known as a method of forming fine patterns in semiconductor device or a micro electro mechanical systems (MEMS) or the like. The nanoimprint is a technology for bringing a mold on which a fine pattern is formed by an electron beam exposure or the like into contact with a substrate formed of a wafer or a glass or the like on which an imprint material (resin material such as resist) is applied, thereby transferring the pattern onto the resin which is the imprint material.
When a nanoimprint is performed, it is necessary to conform a magnification (size) of the pattern formed on the wafer to a magnification of the pattern to be transferred onto the mold. However, the entire wafer enlarges or reduces in the course of heating process such as film formation or sputtering, and as a result, the magnification of the pattern can differ between in X-direction and Y-direction. In actual semiconductor process, variable magnification of the entire wafer on the order of ±10 ppm occurs, and magnification difference between the X-direction and Y-direction on the order of 10 ppm occurs.
In a conventional lithography such as a stepper or a scanner, variable magnification is addressed by altering each shot size during exposure in conformity to a deformation of the wafer. For example, in the case of a scanner, reduction magnification of a projection optical system is altered on the order of several ppm in conformity to a magnification of the wafer, furthermore a scanning speed is altered several ppm in conformity to a magnification of the wafer. In this way even when magnification difference occurs between the X-direction and Y-direction, high overlay accuracy is realized by correcting the magnifications.
However, since there is no projection optical system in the nanoimprint, like in conventional lithography, and the mold and the wafer come into direct contact with each other via a resin, such a correction cannot be made.
Thus, in the nanoimprint, another approach is used to correct a variable magnification of the pattern which is generated during semiconductor process as described above. In order to conform the pattern formed on the mold to a magnification of the pattern of wafer, a magnification correction mechanism for physically deforming the mold is employed. As a method for physically deforming the mold, a method for deforming by exerting an external force from an outer periphery of the mold, or a method for expanding the mold by heating the mold are adopted.
As an application example of the imprint apparatus, lithography of the semiconductor device on the order of 32 nm half pitch is considered. At this time, according to the International Technology Roadmap for Semiconductors (ITRS), overlay accuracy is 6.4 nm. Therefore, it is also necessary to control the magnification correction with accuracy of several nanometers or less.
In the lithography using the imprint apparatus as described above, it is necessary to correct a shape of the pattern to be transferred. For example, distortion can occur on the pattern to be transferred. The causes include the following points. For example, the pattern side faces upward during fabrication, while the pattern side faces downward during usage (during pressing), that is, the mold has different orientations. Consequently, the pattern is deformed by an influence of gravity or the like. Also, when the pattern is formed on the mold by electron beams or the like, distortion of pattern image can occur on the mold due to distortion aberration of an optical system of an electron beam rendering device. Further, even supposing that the pattern of the mold could be manufactured without distortion, the overlay accuracy will become worse if distortion has occurred in the pattern on the substrate. A difference in shapes between the pattern already formed on the substrate and the pattern formed on the mold, which will lead to such a deterioration of the overlay accuracy, is called a distortion (aberration).
In the imprint apparatus, a magnification correction mechanism is mounted to correct these distortions. In the magnification correction mechanism, the mold is physically deformed within an X-Y plane in order to correct the mold in a target shape. However, when a shape of the mold is corrected as illustrated in FIG. 5A, the pattern area will be also deformed in a pressing direction (Z-direction) by its own weight or the like. Further, a deformation amount in the Z-direction varies depending on the shape to be corrected of the mold. Such a deformation in the Z-direction of the mold causes occurrence of pattern distortion during pressing and the overlay accuracy becomes worse.
Japanese Patent Application Laid-Open No. 2010-080714 discusses a control method for inhibiting such a deformation of the mold. According to Japanese Patent Application Laid-Open No. 2010-080714, a mold chuck includes a base portion and a holding portion for holding a plurality of peripheral portions of the mold and a driving mechanism for positioning the holding portion relative to the base portion, and corrects a shape of the mold so as to follow a shape of the wafer by driving the holding portion, thus improving the overlay accuracy.
However, in order to attain an imprint in which accuracy of several nm or less is required even in the magnification correction as described above, there is an additional issue. The issue includes the fact that the pattern will be deformed when the pattern formed on the mold is transferred by being pressed against the substrate, in the imprint apparatus. When the mold is pressed against the substrate as illustrated in FIG. 5B, if the spacing between the mold and the substrate is rendered too small, a large distortion occurs outside the pattern of the mold. Further, if the spacing between the mold and the substrate is rendered too large, similarly a large distortion occurs outside the pattern of the mold. As a result, even when pressed after correcting such that the distortion becomes small by the magnification correction mechanism, the distortion results in occurring by deformation when the mold is pressed. In this case, the overlay accuracy becomes significantly worse especially near the outer periphery portion of the pattern. Therefore, it is necessary to properly determine a distance between the mold and the substrate when the pattern is transferred such that the distortion becomes small in the outer periphery portion of the pattern of the mold.